The present invention relates generally to an improved filament for use in the rotary cutting of weeds and vegetation, and more particularly to such a filament in which the tendency of the ends to fibrillate is significantly reduced. In particular, the filaments of the present invention have been found to possess extremely long lifetimes when utilized as rotary vegetation cutting members.
The cutting of weeds and trimming of grass and other vegetation has normally been accomplished by the use of metal shears, blades, or rotary powered disks. Hand operated shears tend to render the cutting of weeds and trimming of vegetation to be laborious and tedious, and the utilization of powered shears, blades or powered rotating disks has been dangerous, particularly when these devices are utilized by untrained or unskilled persons who do not appreciate the risks and dangers involved in the usage. While numerous attempts have been made to provide shields or guards about the moving components, such shields or guards have normally been deemed undesirable because of the manner in which they inhibit normal use of the apparatus.
Recently, it has been found that a durable monofilament line, when rotated at high rates of speed provides an efficient and safe means for cutting weeds and natural vegetation, and for trimming grass and the like. Rotational rates in the range of from 2,000 to 20,000 r.p.m. are commonly employed. Typical examples of this type of vegetation cutter are described in U.S. Pat. Nos. 3,985,440; 3,928,911; 3,831,278; 3,693,255; 3,018,602; 3,859,776; and 3,708,967. In each of these devices, a flexible filament is normally employed, perferably a monofilament, however flexible strings, cords and twines have also been suggested.
The filaments utilized for this purpose are essentially filaments having a smooth surface, with the monofilamentary products preferably being oriented polymeric materials such as nylon polyamides or the like. While these devices have normally reduced the risks involved in powered cutting apparatus, the continued utilization of the devices has been found to present problems of cutting efficiency.
Specifically, the ends or end portions of the filamentary materials utilized tend to fibrillate, thereby breaking up into a number of small fibers having limited cross-sectional diameters or areas. Since the energy available for cutting is greatest at the tip of the filament, any reduction in cross-sectional area, and effective mass of the filament correspondingly reduces the ability of the filament to sever the vegetation which it strikes. Normally, the severing action is accomplished by means of abrasion of the stalk of the vegetation through impact.
As has been indicated, the preferred material for the filament is a nylon polyamide material, and particularly monofilaments prepared from nylon 6 (polymerized polycaprolactam). While metallic filaments, in either single or multi-braided form, have been proposed, they were found to be exceedingly dangerous to use because of the normally occurring fracturing of the filament, and ultimate tangential discharge of the resulting metallic fragments or particles. Accordingly, attempts were made to provide safe operation of these structures through the use of braided polymeric filaments, or monofilaments. The problems with braided filaments was essentially that these filaments tended to fibrillate, and upon fibrillation, very little tip cutting action was achieved.
Typically, the monofilaments range in size from about 0.030 up to about 0.125 inches. In the past, these monofilaments, specifically nylon monofilaments, were regular in cross-section, and were normally substantially circular. The surface was relatively smooth, similar to that of monofilament used for a fishing line or similar purposes. However, these nylon monofilaments frequently tended to fibrillate under conditions of heavy use, with the exposed tip end of the filament degenerating into a family of tiny fibrils which decreased the cutting efficiency of the filament. Fracturing or casting-off of the fibrils tended to expose blunt ended material which possessed improved cutting performance, however, this improved performance deteriorated when fibrillation again occurred. Accordingly, overall cutting efficiency was frequently and normally reduced during utilization.
An increase in the tendency toward fibrillation occurs whenever the cutting filament strikes the vegetation at a point spaced from the tip end. While this tendency may be reduced through slow movement of the cutter, it has been found that cutting efficiency and speeds are reduced to an impractically low level when slow movement is utilized.